As a method of detecting a doze, conventionally, a method is proposed in which a decrease in an arousal level is detected by detecting a blink burst, which means a state where a plurality of eye closures occur in a short time, for example, within 1 second. For example, Patent Literature 1 discloses a detection method in which it is determined that the arousal degree decreases (it is in a doze state) when a slow eye movement (SEM) which is a lateral movement of an eyeball accompanying closing of the eyelids is detected within a predetermined time from detecting a burst of blink. The burst of blink and SEM are characteristic phenomena appearing in the early stage of sleep onset, and a decrease in arousal degree is determined by the combination thereof.
Patent Literature 2 discloses an arousal decrease detection apparatus that includes a blink detection means that detects a blink of a subject, a blink determination means that determines, among the blinks detected by the blink detection means, a blink in a blink burst in which a blink interval between the blink and the immediately-preceding blink is within a predetermined time and a blink with a long eye-closure for a predetermined time or longer, and an arousal decrease determination means that determines an arousal decrease degree on the basis of a time from the blink of the blink burst to the blink with the long eye-closure.
However, blinks are extracted without distinguishing between normal blinks and a blink burst in the detection method described in Patent Literature 2, and thus, the extraction method is not specialized for a blink burst. Accordingly, in the detection method described in Patent Literature 2, a blink phenomenon, often observed during a blink burst, in which an eye transitions from closed to half-open and then back to closed, cannot be detected, so that there is a problem that blink bursts cannot be detected with high accuracy.
Therefore, in order to detect a blink burst with high accuracy, Patent Literature 3 proposes that a drowsiness assessment device which includes an image capture means that successively captures an image of a region including an eye of an assessment subject, an openness detection means that detects time series data of eyelid openness on the basis of the images successively captured by the image capture means, a blink burst detection means that on the basis of the eyelid openness time series data detected by the openness detection means extracts any maximum values and minimum values from a range in which the eyelid openness is continuously less than a predetermined threshold value and detects blink bursts when a blink interval detected at a threshold value set between an extracted maximum value and an extracted minimum value is within a predetermined time, and a drowsiness state assessment means that assesses the state of sleepiness of the assessment subject on the basis of the result detected by the blink burst detection means.
On the other hand, in Non Patent Literatures 1 and 2, a relation between a closed eye time of the first blink during a blink burst and rated sleepiness is investigated in order to detect a doze state only on the basis of a characteristic of a blink. It is described that, as a result, when an arousal degree decreases, the closed eye time of the first blink becomes longer.